1. Field of the Invention
The present invention relates to an optical head, an optical-information medium driving device and a sensor. Specifically, the present invention relates to a small sensor which detects the tilt or position of an optical information medium, an optical head and an optical-information medium driving device which are provided with this sensor, a sensor which detects the tilt or position of an optical component which needs to be displaced among the component parts of an optical head, and an optical head and an optical-information medium driving device which are provided with this sensor.
2. Description of the Related Art
In today's advanced IT society, technological development has been flourishing for a high-density and large-capacity memory. As capabilities required for such a memory, there are mentioned a high density, a large capacity and high reliability, as well as a rewriting function and the like. As one of those that can satisfy these demands, an optical disk is well known in which information is optically recorded and regenerated, using an optical head. With respect to an optical head, a great number of reports have conventionally been made on the art of detecting the tilt of an optical disk. For example, examined application publication No. 7-82657 describes how to resolve disadvantages in that if an LED (or light emitting diode) and a pair of photo-detectors is provided, costs for an optical head will become higher and its size will be difficult to make smaller.
FIG. 18 describes a configuration of the optical head according to the mentioned examined application publication. Its configuration and operation will be described below.
In FIG. 18, reference numeral 1 denotes a semiconductor laser which is a light source (hereinafter, referred to as the LD); 2, a luminous flux which is emitted from the LD 1; 4, a beam splitter as a splitting means which splits the luminous flux reflected by an optical disk 6 from the emitted luminous flux; 7, an aperture restricting means which restricts an aperture for a luminous flux that is incident upon an objective lens 5 which is used as a converging means; 9, a light spot at which the luminous flux 2 emitted from the LD 1 is converged on an information recording surface of the optical disk 6; 10, a light detector which receives the luminous flux that has been reflected by the optical disk 6 and has passed through the objective lens 5 and the beam splitter 4, and conducts its photoelectric conversion; 40, an optical axis of the objective lens 5; 8, an unnecessary luminous flux except for the effective luminous flux 2 of a luminous flux emitted from the LD 1 which passes through the aperture restricting means 7 and is incident on the objective lens 5 (i.e., a luminous flux for tilt detection, or a luminous flux which is used to detect a tilt of the optical disk 6); 17, a light spot at which the unnecessary luminous flux 8 is converged on the information recording surface of the optical disk 6; 14, a light detector for tilt detection as a second detecting means which receives the luminous flux of the unnecessary luminous flux 8 which is reflected from the optical disk 6; and 90, a reflecting mirror as a travelling-direction changing means which changes the direction in which a part of the unnecessary luminous flux 8 travels so that it is incident upon the objective lens 5 through the aperture restricting means 7. The above described tilt-detection light detector 14 includes two detection areas 14a, 14b. An output from each area 14a, 14b is given to a subtracter 15. This tilt-detection light detector 14 outputs an angle at which the optical axis of the objective lens 5 crosses the information recording surface of the optical disk 6. In other words, it is used to detect a tilt of the optical disk 6.
In FIG. 18, an operation will be described for detecting a tilt of the optical disk 6. The effective luminous flux 2 is determined by the aperture restricting means 7, and is the luminous flux which diverges from the LD 1 and is used for recording and regeneration in the optical disk 6. With respect to the unnecessary luminous flux 8 other than that, the direction in which a part of it travels is changed by the reflecting mirror 90. Then, it passes through the aperture restricting means 7 and reaches the convergent light spot 17 on the optical disk 6 through the objective lens 5. The convergent light spot 17 is irradiated which is a position different from that of the convergent light spot 9 for recording and regeneration. The luminous flux which is reflected from each convergent light spot 9, 17 on the optical disk 6 forms an image in a different position. Then, it is received by the light detector 10 and the light detector 14, respectively. The light detector 14 is used for tilt (i.e., the tilt of an optical disk) detection and is a light detector which is divided in the two detection areas 14a, 14b. The light detector 14 is placed so that if the optical disk 6 is perpendicular to the optical axis of the objective lens 5, the quantity of the tilt-detection luminous flux 8 which is received from the convergent light spot 17 becomes equal at the detection area 14a and at the detection area 14b. In FIG. 18, the radius direction of the optical disk 6 is along the X-axis. If the rotational axis of the optical disk 6 tilts with respect to the Y-axis (i.e., around the Y-axis), the tilt-detection luminous flux 8 moves toward the +X-directions on the light detector 14. Then, the difference between the quantity of the light received by the detection area 14a and the quantity of the light received by the detection area 14b are obtained by executing the following arithmetical processing: (the receiving-light quantity of the detection area 14a)−(the receiving-light quantity of the detection area 14b). Thereby, the tilt of the optical disk 6 can be detected. This tilt information is outputted as a tilt signal VTILT from the subtracter 15. Hence, a luminous flux for tilt detection can be obtained only by providing the reflecting mirror 90 in the unnecessary luminous flux of the LD1 which is not in common use. In short, there is no need to use a separate light source such as an LED.
Herein, none of the components which are not based upon the purport of the present invention are shown in the figure, and their description is omitted. They include an optical head, and other components that configure an optical-information medium driving device which this optical head is applied to, such as an actuator, a motor, a circuit and a mechanism.
However, the configuration of the above-mentioned examined application publication has the following disadvantages. According to the configuration shown in FIG. 18, a luminous flux for tilt detection is obtained without using a separate light source such as an LED. This helps make an optical head smaller by its volume. But, the publication is configured such that the light detector 14 forms an image of the tilt-detection luminous flux 8 at the convergent light spot 17 and receives it. This requires the light detector 14 to sit near the light detector 10. As a result, an additional volume has to be secured from the aspect of the configuration of an optical head. Furthermore, the unnecessary luminous flux 8 of the LD1 is used, and thereby, the quantity of a luminous flux for tilt detection, or the degree to which it diverges, varies according to the peculiarity of an LD1. Consequently, the performance of detecting a tilt (i.e., the tilt of an optical disk) also becomes uneven. Moreover, when the position of the light detector 14 is adjusted, it forms an image at the convergent light spot 17 and receives it. At that time, the receiving-light quantity of the detection area 14a has to be equated with that of the detection area 14b. Hence, it is necessary to adjust the light detector 14 extremely precisely. In addition, the temperature near the LD1 goes up to become higher than any other place in an optical head. This rise in temperature may change the position or direction of the unnecessary luminous flux 8 from the LD1. Thus, the performance of detecting a tilt (i.e., the tilt of an optical disk) may decrease, thereby causing an error. In sum, the fact that there is no need for a separate light source such as an LED presents advantages in that the optical head can be made smaller and its costs can be lowered. However, there are disadvantages in that it cannot be made simple enough and an adequate performance of detecting a tilt (i.e., the tilt of an optical disk) cannot be obtained.
On the other hand, a so-called tilt sensor is also in practical use, which is formed by uniting an LED as a separate light source with a light-receiving element. However, such a tilt sensor has a size of, for example, about 7 mm×7 mm, and 9 mm in height. This makes it difficult to place it in a small optical head.